The Salawati and Bintuni basins are late Tertiary depocentres located in the western-most part of Irian Jaya. The two basins are closely located and only separated by a 50 kms wide structural high known as the Ayamaru Plateau. Petroleum exploration results in the Salawati Basin has been very successful. This basin has produced around 300 million barrels of oil from the Miocene carbonates of the Kais Formation. Exploration with similar objectives in the Bintuni Basin, however, has had only little success. Some oil was obtained from the small Wasian and Mogoi fields which between 1951 to 1960 jointly produced around 7 million barrels oil. Further extensive exploration campaigns between 1970 to 1980, with Miocene Kais Limestone as the objec-tive resulted only in the discovery of Wiriagar Field. The big difference in petroleum potentiality of the Salawati and Bintuni basins has attracted authors to evaluate which significant geological factors that had influenced it. Evaluation of available exploration data of the basins, gave interesting results : In terms of geologic factors necessary for hydrocarbon accumulation (presence of mature source rock, migration, pathway, good reservoir quality, valid trap and effective seal), it seems that shale of Cretaceous age has played the most important role. If this regional seal is absent or non effective, oil could migrate vertically from Pre-Tertiary source to the Tertiary reservoirs. On the contrary, if the Cretaceous shales are present and sealing, then the underlying Mesozoic sequences is attractive and may have trapped hydrocarbons, if supported by other geologic factors.
Authors : Luki Samuel, Lukman K & Suharno